Sleep Glossary

Adjustable base: An electro-mechanical or manual bed frame construction that permits the raising and lowering of the head and/or foot portions of the mattress.

Advance Sleep Phase Syndrome: A circadian rhythm disorder in which the main sleep period is advanced in relation to the desired clocktime, resulting in symptoms of compelling evening sleepiness, an early sleep onset and an awakening earlier than desired.

Altitude Insomia (also referred to as "Acute Mountain Sickness", "Acosta`s Disease", "Alpine Sickness", and "Hypobaropathy"): A form of insomnia that occurs when people travel to higher altitudes, usually accompanied by headaches, loss of appetite and fatigue. Around 25 percent of individuals who move from sea level to 2,000 meters will experience symptoms.

Arousal: Awakening from sleep. Sleep scientists also use this term to refer to the change from a deeper stage of non-REM sleep to a lighter stage

Arousal Threshold: The parameter that measures how easily a sleeping person is awakened.

Bed: Generally refers to a mattress and foundation set.

Bedding: Commonly used as a generic term for a mattress and foundation set, but may also apply to accessory items such as blankets, sheets, pillows, comforters, mattress pads, etc.

Bedding ensemble: A complete sleep support system, consisting of a metal frame or a bed, a foundation and a mattress set.

Bed frame: A metal or wood frame with legs used to support a mattress and foundation. Conventional height is 7-1/4 inches and the low-profile version is 5-3/4 inches when measured from the floor to the bottom of the foundation. Generally a headboard can be attached. Metal frames are sometimes known as a “Hollywood” frame.

Biological Clock: A collection of cells that regulates an overt biological rhythm, such as the sleep/wake cycle, or some other aspect of biological timing. This can include reproductive cycles or hibernation.

Biphasic Sleep: A pattern in which the main sleep period at night is split into two rough halves, with waking periods of an hour of more in between.

Body Impressions: Indentations occurring on the surface of a mattress over time due to the compression of materials by the human body.

Bruxism: Commonly known as teeth grinding or jaw clenching during sleep. The stressful force of clenching causes pressure on the muscles, tissues, and other structures around your jaw.

Comfort system: Refers to the upholstery layers of the mattress, generally consisting of a combination of materials (cover, cushioning, topper pad, insulators, etc.).

Chronotherapy (Also referred to as "light therapy"): The use of bright light to affect a change in sleep patterns. Advocates of chronotherapy claim it affects the same brain chemicals that antidepressant drugs do, with the advantages of being less expensive, quickly working and less side effects.

Circadian Disruption (also referred to as "Circadian Disturbance"): A departure of the body's circadian cycle from the environment or habit, resulting in a change in the time of day during which sleepiness and wakefullness happen. Often caused by jet lag or transitions into and out of daylight savings time, or between workweeks and weekends.

Circadian Rhythm: Relating to or exhibiting approximately 24-hour periodicity, especially related to fluctuation of behavioral and physiological functions, including sleep waking.

CPAP (Continuous Positive Airway Pressure): A machine that helps a person who has apnea breathe more easily during sleep by sending blowing air at a constant, continuous pressure. When sleeping, CPAP patients wear a face mask connected to a pump that forces air into the nasal passages at pressures high enough to overcome obstructions in the airway and stimulate normal breathing.

Delayed Sleep Phase Syndrome: A circadian-rhythm sleep disorder thought to result from the endogenous circadian pacemaker being “stuck” at a later-than-normal phase, relative to the desired sleep-wake schedule.

Deep Sleep: Refers to combined non-REM sleep stages 3 and 4.

Delta Sleep: The stage of sleep in which EEG delta waves are prevalent or predominant (sleep stages 3 and 4). Also referred to as "slow wave" sleep because brain activity slows down dramatically from the "theta" rhythm of Stage 2 to a much slower rhythm of 1 to 2 cycles per second called "delta". During this time, the height or amplitude of the waves increases dramatically.

Delta Waves: Brain waves with a frequency of 1 to 3 hertz that emanate from the forward portion of the brain during deep sleep. Normal amplitude is 75 microvolts

Desynchronization: In the context of sleep studies and disorder diagnosis, refers to lack of alignment between external signals and the biological clock. The cause of many circadian disorders.

Diagnostic Sleep Study: The monitoring of several physiological activities, usually performed to determine the absence or presence of a specific sleep disorder. Diagnostic sleep studies can occur in a sleep disorders center or in a patient's home with portable recording equipment.

Dual-purpose: A broad term used to include all sleep pieces, which can be converted to other uses, including: convertible sofas, high-risers, daybeds, futons, etc. See Convertible Sofa.

Electroencephalogram (EEG): A measurement of the electrical activity associated with brain activity.

Electromyogram (EMG): A measurement of the electrical activity associated with muscle movements. Electromyogram is part of a polysomnogram.

Electroculogram (EOG): a measurement of the electrical activity associated with eye movements. An Electroculogram is part of the polysomnogram.

Entrain: To reset or align with the biological clock.

Enuresis: The act of bed-wetting

Euro-top mattress: A mattress featuring a raised, squared-off surface finishing treatment filled with soft comfort layers and attached to the mattress upholstery at the tape-edge.

Excessive Daytime Sleepiness (also "excessive daytime somnolence"): Subjective report of difficulty in staying awake, accompanied by a ready entrance into sleep when the individual is sedentary. While EDS suggests the presence of a sleep disorder, it is different from fatigue. Depression, anxiety, stress, and boredom are commonly thought to cause excessive sleepiness, but in fact these conditions cause fatigue and apathy.

Endogenous Rhythms: Rhythms driven by an internal, self-sustaining biological clock rather than by signals that are external to the organism (for example, light).

Exogenous Rhythms: Rhythms that are directly regulated by an external influence, such as an environmental cue. They are not generated internally by the organism itself.

Fatigue: A feeling of tiredness, weariness or lack or energy, usually associated with lower performance (physical or mental). Fatigue is different from drowsiness. In general, drowsiness is feeling the need to sleep, while fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of indifference or not caring about what happens) can be symptoms of fatigue. Fatigue often develops in response to physical exertion, emotional stress, boredom, or lack of sleep.

Headboard: An upright unit of wood, metal, plastic, or upholstered material, to be attached at the head of a bed, usually with the bed frame.

High-contour mattress: Measures 9” – 13” thick. A mattress under 9” thick is considered “standard”; over 13” thick is considered “custom.”

Cataplaxy: Sudden muscle weakness associated with narcolepsy. It is often triggered by emotions such as anger, surprise, laughter, and exhilaration. Cataplaxy is not a black out or a fient because no loss of consciousness is invloved. During cataplaxy, you are fully conscious; however, you can not move.

Hypnic Jerk: A startle reaction as a person falls asleep; muscle jerks like an electric shock. Normal. Everyone experiences them. Also called a sleep start or a hypnagogic jerk.

Hypophobia: A general term for the fear of sleep. Hypophobia is considered an anxiety disorder, rather than a sleep disorder.

Insomnia: A sleep disorder in which those affected complain of having difficulty in sleeping. People with insomnia have one or more of the following symptoms:

Hypersomnia: Excessive sleep, characterized by recurrent episodes of unusual daytime sleepiness or prolonged nighttime sleep. Hypersomnia is different from feeling tired due to lack of or interrupted sleep at night. Those affected are compelled to nap repeatedly during the day, often at inappropriate times such as at work, during a meal or in conversation.

Light Therapy: A form of therapy where the person is exposed to bright light at the appropriate time of day to effect the timing, duration and quality of sleep.

Light Sleep: A term used in clincial practice to describe non-REM stage 1, and sometimes stage 2 sleep. People in light sleep drift in and out of sleep and can be awakened easily. Eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images rather than narrative dreams. Many also experience sudden muscle contractions called hypnic myoclonia, often preceded by a sensation of starting to fall.

Mattress: A manufactured product to sleep on, consisting of various resilient materials covered with an outer ticking. Comes from the Arabic term “matrah” meaning to throw down. Early Arabs traveled with their bedding and threw it down on the ground or floor at night.

Melotonin: A hormone secreted by the pineal gland that is derived from the amino acid tryptophan, which helps synchronize biological clock neurons in the suprachiasmatic nucleus.

Micro-Arousal: Partial awakening from sleep. An episode where a sleeper partially awakes; however, he or she is not aware of it

Micro-Sleep: A period lasting up to a few seconds, during which people appear to be asleep in otherwise waking periods. Cause for concern for people in critical jobs like truck drivers or pilots.

Multiple Sleep Latency Test (MSLT): A common sleep test given at sleep labs in the diagnosis of sleep disorders. The multiple sleep latency test records brain waves (via EEG), heart rate (via EKG), muscle activity and eye movements. Often given as a series of "nap tests".

N1: Stage 1 of sleep (NREM Stage 1

N2: Stage 2 of sleep (NREM Stage 2)

N3: Stage 3 of sleep (NREM Stage 3)

Nap: A short period of sleep at a time separate from the major sleep period, especially during the day

Narcolepsy: A sleep disorder characterized by brief attacks of deep sleep, and with symptoms including excessive sleepiness, cataplexy, sleep paralysis, hypnogogic hallucinations, overwhelming daytime sleepiness (even after adequate nighttime sleep), and an abnormal tendency to pass directly from wakefulness into REM sleep. See page on narcolepsy.

Night Terrors (also referred to as "Sleep Terrors" or "Pavor Nocturnus"): The incomplete arousal from slow wave sleep ,accompanied by a state of intense fear and agitation. During a night terror, the person awakens in terror with feelings of anxiety and fear but is unable to remember any incident that might have provoked those feelings.

Nocturnal Sleep-Related Eating Disorder (NS-RED): The act of eating while sleepwalking. Typically the person doesn't remember eating when he or she wakes up.

NREM (Non-REM sleep): A normal part of sleep, accounting for typically 75-80% of sleep time. Characterized by slower and larger brain waves than in REM. By larger, we mean greater amplitude in the EEG output.

Obstructive Sleep Apnea (OSA): A disorder in which breathing is frequently interrupted for brief intervals during sleep, resulting in intermittent decreases in blood oxygen levels and transient arousals from sleep, leading to poor sleep quality and excessive daytime sleepiness.

Paradoxial Sleep: REM Sleep

Photoperiod: The light/dark or day/night cycle.

Parasomnias: Sleep disorders that intrude into the sleep process and create disruptive sleep-related events. These behaviors and experiences occur usually during sleep and are most often infrequent and mild

Pillow-Top Mattress: A mattress featuring a surface finishing treatment where a separate encasement of soft materials is attached to the entire surface on top of existing cover and upholstery.

Polysomnograph: A test of sleep cycles and stages through the use of continuous recordings of brain waves (EEG), electrical activity of muscles, eye movement (electrooculogram), breathing rate, blood pressure, blood oxygen saturation, and heart rhythm and direct observation of the person during sleep.

Sheeting: a woven or non-woven fabric other than knits that have a degree of sizing and are somewhat stiff.

Quiet Sleep: A Non-REM sleep

Rapid Eye Movement Sleep (REM Sleep): A deep sleep period with rapid eye movements. REM Sleep is a normal part of sleep cycle. It recurs cyclically several times during a normal period of sleep. Characterized by increased neuronal activity of the forebrain and midbrain and by depressed muscle tone. Most dreaming occurs in this stage, which accounts for about 20 percent of sleep in adults.

Rebound Sleep: Sleep difficulties after discontinuing use of a hypnotic medication.

REM Motor Atonia: When the large skeletal muscles go limp during REM sleep.

REM Period: The REM portion of a NREM-REM cycle. When the period occurs early in the night, it may be as short as a half-minute. when the period occurs later cycles longer than an hour.

REM Sleep Behavior Disorder (RBD): A very rare disorderm, in which the sleeper acts out dreams, often violently, and has bodily movement.

REM Sleep Rebound: An increase in REM sleep following unnatural reduction. Extension of time in, and an increase in frequency and density of REM sleep episodes.

Restless Leg Syndrome (RLS): A sleep disorder characterized by a deep creeping, or crawling sensation in the legs even when the legs are not moving. There is an almost irresistible urge to move the legs; the sensations are relieved by movement.

Sleep Fragmentation: Sleep interruption due to frequent, sustained awakenings or early morning awakenings

Sleep Hygiene: The conditions and practices that promote continuous and quality sleep. Sleep Hygiene includes bedtime routines, regular bed and arise times, as well as, regularly receiving enough sleep to avoid sleepiness during the day. For more on sleep hygiene, please visit our sleep tips page.

Sleep Inertia: Feelings of grogginess and/or sleepiness that persist longer than 10 to 20 minutes after waking up. Symptoms includ transitory "hypovigilance" or low vigilance, confusion, disorientation of behavior and impaired cognitive and sensory-motor performance. Oftentimes, sleep inertia occurs when a person is aroused from deep sleep in the first part of the night.

Sleep Latency: The time between going to bed and sleep onset.

Sleep Maintenance: The ability to remain asleep for a long period of time

Sleep Paralysis: The temporary inability to talk or move when falling asleep or waking up.

Sleep Talking: The utterence of speech or sounds during sleep without awareness of the event. Sleep talking occurs during stage REMS, representing a motor breakthrough of dream speech. Sleep talking can also occur in the course of transitory arousals from NREMS and other stages.

Sleepiness (also referred to as "somnolence" or "drowsiness"): The state where the subject finds it difficult to maintain the wakeful state and falls asleep if not actively kept aroused. Sleepiness differs from a feeling of physical tiredness or listlessness.

Sleepwalking (also referred to as "somnambulism"): A sleep disorder where the person gets out of bed and walks around during sleep. Sleepwalking typically occurs in the first third of the night, during deep NREM sleep (stages 3 and 4).

Somniphobia: The fear of sleep or fear of falling asleep. Somniphobia is an anxiety disorder.

Somnolence: More commonly known as drowsiness, especially when the person seems on the verge of falling asleep.

Snoring: The noise produced with inspiratory respiration during sleep. Snorng is the vibration of the soft palate and the pillars of the oropharyngeal inlet. Around 45 percent of normal adults snore occasionally, and 25 percent are habitual snorers.)

White Noise: The heterogeneous mixture of sound waves extending over a wide frequency range. White noise may be used to mask unwanted noise that may interfere with sleep.